1. Field of the Invention
The present invention relates to a ring-shaped light emitting unit. The invention is used to decorate speaker grilles or watches or speedometers or tachometers of vehicles (automobiles, trains) or aircraft.
2. Description of the Related Art
There is an increasing tendency to try to decorate various objects (for example, interior products of vehicles) with light based on the background that light sources such as LEDs which consume less power are now allowed to be used and that the adherence of consumers to design is increased. As part of the tendency, light emitting units are under development in which a ring-shaped light is obtained by utilizing a ring-shaped light guiding body and a light source in combination. One example of related ring-shaped light emitting units is shown in FIG. 7 (refer to JP-A-2004-14122). In the example shown in FIG. 7, a light guiding path 53, which introduces light of a light source 52, is formed in such a manner as to continue to an outer circumferential portion of a ring-shaped light guiding member 51, whereby the light of the light source 52 is introduced into the ring-shaped light guiding member 51 through the light guiding path 53 from a circumferential (lateral) direction. According to the light introducing method like this, the introduced light is allowed to travel along a direction in which the ring-shaped light guiding member 51 extends efficiently. However, part of the light is lost during the passage thereof through the ring-shaped light guiding member 51, whereby a portion of the light guiding member 51 in the vicinity of a light inlet portion tends to be illuminated brightly in any way, whereas the light guiding member 51 extends farther away from the vicinity of the light inlet portion, it tends to get darker. To cope with this problem, a method has been considered in which the insufficient luminance at an area farther away from the light inlet portion is compensated for by gradually changing the width of the ring-shaped light guiding member by changing the curvature of an outer circumference of the light guiding member. In this method, however, a convergence of light is caused due to the change in the curvature of the outer circumference, and as a result, there is caused a problem that an emission line is caused to appear.
On the other hand, as shown in FIG. 8, there have been proposed methods in which light is introduced from a lower surface 62 of a ring-shaped light guiding member 61 (refer to JP-A-2003-297107 and JP-A-2003-297108). In a method shown in FIG. 8A, light of a light source 52 is directly introduced into a ring-shaped light guiding member 61. Then, lights directed in two leftward and rightward directions are produced from the light so introduced by the action of a light deflecting means 63. In a method shown in FIG. 8B, a light guiding path 66 is provided perpendicularly on a lower surface 62 of a ring-shaped light guiding member 61. In this configuration, lights directed in two leftward and rightward directions are produced from light introduced into the ring-shaped light guiding member 61 via the light guiding path 66 by the action of a light deflecting means 63. Thus, in these configurations, light is designed to reach to everywhere in the entirety of the ring-shaped light guiding member 61 by making use of the light deflecting means 63. However, since the light deflecting means 63 is formed in the ring-shaped light guiding member 61, this causes a problem of badly affecting the light guiding effect, and as a result, the luminance of light emitted becomes uneven. In particular, there is caused a problem that a cut line is observed in the light guided.